fnmatch breaks referential transparency

[fpringle]

fnmatch gives different outputs on successive calls with the same inputs:

ghci> import FnMatch as F
ghci> F.fnmatch "a" "a" []
False
ghci> F.fnmatch "a" "a" []
True

fnmatch version: 0.1.0.0
GHC version: 9.2.8
System: NixOS 23.05

[domenkozar]

❯ stack ghci
Configuring GHCi with the following packages: fnmatch.
GHCi, version 9.6.3: https://www.haskell.org/ghc/  :? for help
[1 of 1] Compiling FnMatch          ( /home/domen/dev/fnmatch/src/FnMatch.hs, interpreted )
Ok, one module loaded.
Loaded GHCi configuration from /home/domen/.cache/stack/ghci-script/1fc6c52b/ghci-script
ghci> import FnMatch as F
ghci> F.fnmatch "a" "a" []
True
ghci> F.fnmatch "a" "a" []
True
ghci> F.fnmatch "a" "a" []
True
ghci>